A 19-year-old girl was admitted to our hospital because of general fatigue, headache and purpura. A number of her laboratory findings suggested hemolytic anemia and thrombocytopenia. Direct/indirect Coombs tests gave negative results. Although the patient had no neurological or renal abnormalities, peripheral blood smears showed marked red cell fragmentation, and therefore she was diagnosed as having thrombotic thrombocytopenic purpura (TTP). Fresh frozen plasma (FFP) was transfused daily. The thrombocytopenia and hemolysis immediately improved, but worsened again after reduction of the FFP transfusion. Plasma exchange was instituted every other day, but the patient's condition worsened. Palsy and consciousness disturbance developed, and finally she lapsed into a coma. Daily plasma exchange and methylprednisolone pulse therapy were performed, together with weekly vincristine therapy, and this led to a gradual improvement in the patient's condition. However, several attempts at weaning from plasma exchange resulted in exacerbation of the TTP activity. Therefore oral cyclosporine A was started and splenectomy was performed. After these interventions, despite transient relapse, the patient was successfully weaned off the FFP transfusion, and she is now in remission. Because in this case splenectomy and cyclosporine A resulted in sustained remission of TTP that was refractory to intensive plasma therapy, an autoimmune mechanism may have been involved in the pathogenesis.